Tubular plastic product is extruded using a die head connected to a supply of molten plastic with the die head applying pressure and advancing the molten plastic to the die tooling located at the discharge outlets of the die head. Die tooling is used to receive the molten plastic and guide the molten plastic to an extrusion outlet. In the die tooling for the extrusion of tubular product, the die tooling typically includes an outer cylinder member in cooperation with a coaxial inner cylindrical member whereby a cylindrical extrusion passage is defined or a multiple of this there between. At the downstream end of the die tooling, a restrictor is typically provided that defines a restricted extrusion outlet. Where the tubular product is a double walled tubular product, a second die head passage is used and a second extrusion passage defined by a third cylindrical member is provided in the die tooling. The molten plastic is provided to a second extrusion outlet typically located downstream of the first extrusion outlet.
Die tooling for extruding single or double wall pipe is expensive to manufacture and requires the use of spiders to interconnect the various cylindrical components and maintain a particular relationship there between. These spiders are located in the flow stream of the molten plastic and are designed to minimize disruption of the flow of plastic. These spiders are of a specialized shape and serve to mechanically connect the extrusion sleeve holes for air type members. Assembly of the components to reduce variations also requires care.
In addition to the die tooling being relatively costly to manufacture and assemble, it may also be vulnerable to damage. If excess pressures occur in any of the various extrusion passages, the actual die tooling can be distorted and damaged.
The present invention provides an alternative arrangement that has been found effective in use and has certain advantages over the accepted technology.